US-A-2003042354 describes the use of strain transducers throughout the structure of an aircraft, and analysis of their outputs to detect a hard landing. Various locations for the transducers are described including a trunion bolt which is deflected in bending. If a signal from a transducer exceeds its criteria then a processor illuminates an indicator light for the appropriate landing gear.
WO-A-0039542 describes a pin bearing with strain gauges which are used to measure ground loads applied to such pin bearings in aircraft landing gear.
A problem with the method employed in US-A-2003042354 is that it is difficult to achieve a reliable detection of a hard landing. If the “criteria” are set too high then there is a risk of not detecting a hard landing, but if they are set too low then there is a chance of generating a false indication of a hard landing.